Yet another gantry CNC router.

[routercnc]

I'm pretty sure Dean runs without a lower Z limit switch for similar reasons you have mentioned above. I also ran without limit and Z home switch for a while as I kept getting false e-stops (longest cables, direct into BoB), but my 24V upgrade should sort that out. You'll have to decide what you are comfortable with.

You could locate the 'lower' limit switch right at the top near the stepper motor housing, then connect a long upside-down 'L' shaped bracket to the Z axis so that when it gets near the bottom the bit of the 'L' which sticks out comes down and presses the top of the switch. This might look a bit untidy but its an option and is well out of the way of the swarf.

If you've been following the recent build logs you'll see some useful circuit diagrams for wiring limits etc. which avoids the problem you mention above. Once you get the bugs out (which is normal by the way!) I think you have a nice little machine there.

Been meaning to ask (as I'm about to do the same) - did you finish the top of the bedplate yourself on another machine or did you have it polished? I can't see machining marks or witness marks at the extremes of travel so I'm guessing you haven't leveled it using the cnc machine?

[cambesol]

The bedplate is 12mm ecocast. It is mounted in a way that I can adjust in situ then clamp it tight. I use a digital indicator mounted in the spindle and have achieved a parallelism of +/- 0.05mm across the table.
I didn't like the finish on the ecocast as it showed every little touch (just wiping swarf left marks) so I used a scouring pad + WD-40 to buff if to a uniform bright finish. This can be achieved every time I want to give it a quick polish.

I am undecided about z-limit. Will have a long look tomorrow.

[Boyan Silyavski]

Isn't it designed to hard stop? I design Z axis so that it looks it would fell from bearing rails, but in reality at a certain moment the ball screw would stop it up or down so the drive will trip if we come to that.
So i agree with all, no switches are needed. Plus you have software limits. Plus you are with Lunix so no excuse on part of software.

[mitchejc]

Congrats, its a VERY nice build, well done! I can imagine lots of hours going into those great looking alu parts! I just love the neat looks of an all aluminium build. Very good suggestion by Silyavski, maybe put a little block of wood or plastic to hard stop it just to prevent it running off the rails if required and ditch the lower Z switch.

Sorry, I don't want to stray too far from the topic but since you have first hand experience, whats your opinion of LinuxCNC so far?

[cambesol]

Congrats, its a VERY nice build, well done! I can imagine lots of hours going into those great looking alu parts! I just love the neat looks of an all aluminium build. Very good suggestion by Silyavski, maybe put a little block of wood or plastic to hard stop it just to prevent it running off the rails if required and ditch the lower Z switch.

Thanks! From start to finish has been around eighteen months which included the control system and liquid cooling. The machining took around 9 months but this is only five hours per week due to work/family commitments. I prefer face-milled aluminium rather than lots of extrusion because it looks nice. Not the fastest way to go, but worth it in the end. It does have a hard-stop, the spindle will not drop onto the table.

Sorry, I don't want to stray too far from the topic but since you have first hand experience, whats your opinion of LinuxCNC so far?

I use Linux a lot (I develop embedded software, drivers etc running on Linux of all flavours) so for me it was a natural choice. I really like LinuxCNC, the work flow I described in the first post has yielded good results although I haven't produced anything that I want to post on this forum yet due to the f*****g limit switch causing random paths to be followed (design flaw, please don't ask - too embarrassing). Today I have drawn up some replacement parts made in acrylic which should fix the problem. I will post a picture when I have my final test piece finished this week.

Linux is not for everyone as it can be frustrating trying to figure out what you need to know to fix a problem. LinuxCNC, once configured, works very well indeed.

In a few months I want to dig deeper into BlenderCAM as it can produce some incredible results. The UI on Blender is a bit of a nightmare though and the learning curve is significant so for the moment I am sticking to 2.5D designs.

[mitchejc]

Good to know. Are you running via a parallel port BOB or are you using one of the smarter usb/ethernet controllers?

I have not really looked into it but first prize for me would be if one can run LinuxCNC on the new Raspberry Pi2 to do the trajectory planning and maybe offload the pulse generation to something else. With your experience maybe something you can do for us